1. Field of the Invention
This invention generally relates to a method of treating waste liquids from photographic processings and more particularly it relates to a method of treating photographic waste liquids containing ferricyanide ions and/or ferrocyanide ions.
2. Description of the Prior Art
Some photographic processings containg a bleaching step. In the bleaching step metallic silver formed by development is converted into silver ions using an oxidizing agent, and such a step is included in processings for silver halide color photographic materials and reducers for photographic printing materials.
The inventors previously proposed to treat waste liquids from photographic processings containing ferricyanide ions and/or ferrocyanide ions with a weakly basic anion exchange resin for removing the ferricyanide ions and/or the ferrocyanide ions (Japanese patent application No. 92,115/1971 and Japanese Patent Application No. 22,907/1972). The methods as disclosed in the above patent applications may be superior to conventional methods in the point of removing ferricyanide ions and/or ferrocyanide ions, but if the ion-exchange resins used in these previous treatments are reused after being regenerated, the ion-exchange capacity of the ion-exchange resins gradually becomes lower and thus the removal of feriicyanide ions and/or ferrocyanide ions becomes inefficient. Accordingly, by these conventional methods the cost of waste liquid treatment becomes high.
To overcome these difficulties, a means of modifying the ion-exchange resins may be encountered, but at present, materials superior to weakly basic anion-exchange resin have not been found.
An object of this invention is, therfore, to provide an efficient and economic method of removing ferricyanide ions and/or ferrocyanide ions in waste liquids from photographic processings.
Another object of this invention is to provide an efficient and economic method of removing ferricyanide ions and/or ferrocyanide ions from a waste reducer liquid.
The inventors have discovered that the above objects of this invention can be achieved by contacting such waste liquids containing ferricyanide ions and/or ferrocyanide ions with a weakly basic ion-exchange resin in the presence of ammonium ions and thiosulfate ions.
The method of this invention will now be explained by referring to an example of treating a photographic reducer. A reducer is used for correcting or reducing the developed density of excessively exposed or excessively developed images or fringed or fogged images which are undesirable for making printing masters, or is used for controlling the gradation of dot images. As such reducers, there are known a Farmer's reducer, a combination of iodine and alkali cyanide reducer, a cerium sulfate reducer, a potassium persulfate reducer, a potassium permanganate reducer and the like. The reducing treatment is described in detail in Erwin Gaffe; "Halftone Photography For Offset Lithography", pages 140-146, published in 1960 by the Lithographic Technical Foundation Inc., New York, New York.
The most commonly used reducers contain ferricyanide and thiosulfate as is well known in the art. Other components are usually present in negligible proportions. The reducers are different from each other only in the concentration of ferricyanide and thiosulfate. Recently, such reducers have been called Farmer's reducers in the art, often comprising potassium ferricyanide and sodium thiosulfate. If a used Farmer's reducer is contacted with a weakly basic anion-exchange resin, ferri-and ferrocyanide in the reducer are adsorbed on the resin and removed from solution. The resin is then treated with an alkaline solution to recover the ferri-and ferrocyanide. However, with repeated absorptions and recoveries, the recovery efficiency of the ferricyanide ions and/or the ferrocyanide ions is gradually reduced.